1. Field of the Invention
Because of their low surface energy non-polar materials are difficult to bond, even with cyanoacrylate adhesives. Particularly difficult to bond are linear polymers of simple olefins, such as polyethylene, polypropylene, polybutene and the like, including their copolymers. Other materials which can be bonded by this invention are polyacetals, plasticized polyvinyl chloride, polyurethane, ethylene-propylene diene polymer thermoplastic rubbers based on vulcanized polyolefins and the like.
While it is well known that solutions of amines and other organic and inorganic bases will accelerate the cure of cyanoacrylate adhesives, it is surprising that the primers of this invention also confer adhesion on non-polar substrates. The curing or polymerisation of a film of cyanoacrylate, between two materials, does not necessarily result in a strong bond, particularly if the materials are non-polar, and if the polymerisation of the cyanoacrylate is excessively rapid, a very weak bond or no bond will result.
2. Description of the Related Art
Various surface treatments have been used heretofore to improve adhesion of the difficult-to-bond materials described above. These treatments include surface abrasion, corona discharge (J.C. Von der Heide & H.L. Wilson, Modern Plastics 38 9 (1961) P199), flame treatment (E.F. Buchel, British Plastics 37 (1964) pl42), U.V. radiation (Practising Polymer Surface Chemistry, D. Dwight, Chemtech (March 1982) P166), plasma treatment, hot chlorinated solvents, dichromate/sulphuric acid and chlorine/U.V. radiation (D.Brewis & D.Briggs, Polymer 22 7 (1981) and references therein). All the above treatments are effective to some degree and are generally thought to work by introducing polar groups on non-polar substrates.
While the above treatments may, on occasion, improve the ability of difficult substrates to be bonded with adhesives, the treatments have the disadvantage of requiring specialized apparatus and equipment and can involve corrosive and/or hazardous materials.
Apart from the above treatments, there are examples in the prior art of the use of various accelerators or initiators of the polymerization of the cyanoacrylate monomer. The disadvantage with such accelerators or initiators is that while the speed of cure of the bond is increased, adhesion on non-polar substrates is not promoted and the resulting bond can be very weak and the adhesive can slip off the substrate.
U.S. Pat. Ser. No. 3326742 of Sheppard discloses the use of certain N-Halogenated compounds at temperatures of at least 90.degree. C. as a surface treatment for organic high polymers to render the surface of the plastic mode adherent, so that the material can be easily and securely bonded with conventional bonding agents or adhesives. The N-Halogenated amine compounds suitable for use in this process are electro-negative organic amine compounds halogenated at the nitrogen atom with either chlorine or bromine. The halogenated amine compound may either be applied to the surface to be bonded or it may be incorporated into the adhesive.
The invention is suitable for use with polymers which are normally difficult to bond particularly polyesters, polyacetals, polycarbonates, vinyl polymers, polyolefins, various nylons, and polyurethanes. Such a surface treatment requires extremely high temperatures which makes it unsuitable for use in a consumer market; it is more appropriate in an industrial setting.
Accelerators comprising basic organic nitrogen compounds for use with cyanoacrylate adhesives for surgical use are disclosed in U.S. Pat. Ser. No. 3483870 of Coover and Fassett. The organic nitrogen compounds are beta-substituted ethyl-amines of formula: ##STR1## wherein R.sup.1 can be alkyl or cycloalkyl of 4 to 6 carbon atoms but, preferably, is phenyl or phenyl substituted with hydroxy or lower alkoxy, or the like, R.sup.2 is hydrogen, lower alkyl, preferably methyl or hydroxyl. R.sup.3 and R.sup.4 are hydrogen or lower alkyl; and at least one of R.sup.2, R.sup.3 and R.sup.4 is hydroxyl or lower alkyl. These compounds are vasoconstrictors and local anesthetics; a particularly preferred compound being epinephrine.
Japanese Patent No. 74012094 of Toa Gasei Chemical Ind. discloses the use of one or more of diethyl amine, o-phenylene diamine, dimethyl-para-toluidine, diethyl-para-toluidine, N,N-diethyl aniline, trichloroacetamide and succinic acid imide to improve adhesion of alpha-cyanoacrylate type adhesives. The compounds may be used either independently or in combination or as a mixture with other amines, and are preferably used as a dilute solution with a solvent. The compounds are particularly suitable for use in bonding light metals, nylon or Delrin (polyacetal resin).
The use of alkalis to promote the adhesion of synthetic resin substances with alpha-cyanoacrylate adhesives is disclosed in Japanese Patent Publication No. 43-5004, of Toa Gosei Kagaku Kogyo Co. Ltd. inorganic or organic basic substances can be used, the most preferred being a caustic aqueous alkali solution with a density of 1 to 20%. Also disclosed are inorganic basic substances such as alkali carbonate and calcium hydroxide, or amides such as dimethyl acetoamide and formamide, amines such as monoethanal amine and ethylamine and other organic basic substances such as piperidine and pyrroline. Many of the substances disclosed in this patent application are caustic and would therefore be unsuitable for use in a consumer product.
A hardening accelerator for use with cyanoacrylate adhesives comprising an amine compound, with a boiling point of between 50.degree. C. and 250.degree. C., together with a deodorizer and a solvent, is disclosed in Japanese Patent Application No. 59-66471 of Toa Gosei Chemical Industry Co. Ltd. Examples of suitable amines are triethyl amine, diethyl amine, butyl amine, isopropyl amine, tributyl amine, N,N,-dimethyl aniline, N,N-diethyl aniline, N,N-dimethyl-p-toluidine, N,N-dimethyl-m-toluidine, N,N-dimethyl-o-toluidine, dimethyl benzyl amine, pyridine, picoline, vinyl pyridine, ethanolamine, propanolamine and ethylene diamine.
Japanese Patent Application No. 48-78961, also in the name of Tao Gosei Chemical Industry Co. Ltd., discloses the use of quaternary ammonium salts as adhesion promotors with inert or non-polar and/or highly crystalline plastics which are normally hard to adhere. The specification discloses a number of suitable compounds such as alkyl ammonium salts, amide-bonded amonium salts, ester-bonded ammonium salts, ether-bonded ammonium salts and alkylimidazolinium salts. The compounds also have use in promoting bonding of porous materials such as wood, leather, paper etc.
U.S. Pat. Ser. No. 3260637 of von Bramer discloses the use of a range of organic amines (excluding primary amines) as accelerators for cyanoacrylate adhesives, particularly for use on metallic and non-metallic substrates. The amines are selected from poly N-vinyl pyridine, poly(ethylenediamine) and an amine of the formulae: ##STR2## wherein R is a C.sub.1-8 alkyl, phenyl, tolyl, xylyl, benzyl, phenylethyl, cyclopentyl or cyclohexyl radical, R.sub.1 is a hydrogen atom, C.sub.1-4 alkyl, phenyl, tolyl, xylyl, benzyl, phenylethyl, cyclopentyl or cyclohexyl radical, R.sub.2 is a C.sub.1-8 alkyl or C.sub.1-8 alkenyl radical, R.sub.3 is a hydrogen atom or a C.sub.1-8 alkyl radical and R.sub.4 is a radical --CH.sub.2 CH.sub.2 --O--CH.sub.2 CH.sub.2 --.